Plant Diseases/White stuff on leaves

I have 2 citrus plants in pots. They both have a white substance underneath the leaves. Some of the leaves are curled on the Orange plant. It does not look like bugs. I have wiped it off and it doesn't come back to that particular leaf. I am wondering what I can do to get rid of this.

AnswerThese look like mealybugs or possibly juvenile scale insects. Scale insects are problems for most citrus plants. (I have the same thing in my greenhouse.) Whether mealybugs or scale insects, the treatment is the same. In small infestations, insecticidal soap solution and an old toothbrush will do the trick. Check local garden center, and look for potassium salt-based insecticidal soap. If you cannot find it, then a solution of mild soap and water will do the trick. If you have a huge infestation, a systemic insecticide or a horticultural oil (for example, Volck oil) treatment would be appropriate. If you plan to eat fruit from these trees, then the systemic insecticide MUST be approved for use in agricultural applications.

Be certain to follow label instructions carefully if you use the chemical control measures.

Expertise

I can help with identification and possible treatment of plant diseases that affect houseplants and horticultural species, to include both biological (fungal, bacterial, viral, parasitic etc.) and environmental/cultural (watering, potting media, etc.) aspects.

Experience

Practical experience with a wide variety of houseplants and greenhouse plants, including cacti, euphorbia, african violets, amaryllus, and many others.

OrganizationsAmerican Phytopathology Society
American Society of Plant Biologists
American Society for Virology